1. Field of the Invention
The present invention relates to a wheel support bearing assembly for rotatably supporting a vehicle wheel such as used in automotive vehicles.
2. Description of the Prior Art
Hitherto, as a wheel support bearing assembly, the assembly has been known, in which a rotatable member is made up of a hub axle and an inner race press-fitted externally onto the hub axle. In this type of the wheel support bearing assembly, in order to facilitate the fixture of the inner race, an inboard end of the hub axle is staked radially outwardly so as to be brought into contact with an end face of the inner race, so that the inner race can be fixed on the hub axle under an axially preloaded condition.
However, under a condition in which a heavy load occurs during, for example, turning of an automotive vehicle, the inner race fixed on the hub axle undergoes a creep, accompanied by an increase of a bearing gap between the inner race and the hub axle which eventually leads to a short lifetime.
In view of the foregoing, as a wheel support bearing assembly designed to eliminate such inconveniences, what is shown in FIG. 7 has been suggested. See, for example, the Japanese Laid-open Patent Publication No. 2001-18604. This wheel support bearing assembly is such that a hub axle 38A and an inner race 38B mounted on an outer peripheral surface of an inboard end of the hub axle 38A are plastically coupled with each other by forming indentations 37 in one or both of the hub axle 38A and the inner race 38B and then by staking radially outwardly the inboard end of the hub axle 38A to increase or expand the diameter of the inboard end or by staking radially inwardly the inner race 38B to decrease or restrict the diameter of the inner race 38B. For the indentations 37, helical indentations such as screws, twill-lined knurls and serrations can be enumerated.
Also, as a wheel support bearing assembly for the support of an automotive drive wheel, what is shown in FIG. 12 has been suggested. See, for example, the Japanese Laid-open Patent Publication No. 9-164803. This bearing assembly is of a structure, in which a two-row of balls 25 are interposed between opposed raceway surfaces 23 and 24 in outer and inner members 21 and 22, respectively, and the inner member 22 is made up of a hub axle 29 having a wheel mounting flange 29a formed on an outer peripheral surface thereof and an inner race 30 mounted externally on an inboard end of the hub axle 29. The inner race 30 is mounted on a step 35 provided in the hub axle 29. A stem portion 33a of an outer race 33 of a constant velocity universal joint is inserted into and splined to a center bore 31 of the hub axle 29, with a step 33b of the outer race 33 urged against an inboard end face 30a of the inner race 30. In this condition, by threading a nut 34 onto a tip of the step portion 33a, the inner member 22 is axially fastened with the outer race 33 and the nut 34.
In this type of the wheel support bearing assembly, it is demanded that the inner race 30 mounted on the hub axle 29 will not drop out before the bearing assembly is mounted on an automotive vehicle. Responsive to the demand, a step 36 is formed in an inner peripheral surface of an inboard end of the inner race 30 and is held by a staked portion 29b provided in an inboard end of the hub axle 29 over the entire circumference thereof.
The wheel support bearing assembly in FIG. 12 is intended to achieve the following improvements. Namely, in the conventional standard wheel support bearing assembly for the support of the drive wheel, the step 36 of the inner race 30 shown in FIG. 12 is not provided and instead the end face of the inner race 30 is directly held by the staked portion 29b. In such case, since the staked portion 29b protrudes axially beyond the inner race 30, an additional machining to provide the staked portion 29b with an abutment face with the outer race 33 of the constant velocity universal joint is required in the conventional standard bearing assembly after the staking process. With the bearing assembly in FIG. 12, the staked portion 29b does not protrude outwardly from the step 36 of the inner race 30 and the end face of the inner race 30 can be used as an abutment face, requiring no additional machining.
However, with the wheel support bearing assembly disclosed in the Japanese Laid-open Patent Publication No. 2001-18604, there is a problem that machining of the indentations 37 required to plastically couple the hub axle 38A and the inner race 38B together requires a great deal of time, resulting in increase of the cost.
Also, the wheel support bearing assembly in FIG. 12 has the following problems.                (1) During the staking process, a staking tool interferes with an inner peripheral surface of the inner race 30, making it difficult to accomplish the staking. In this staking process, unlike the standard orbital forming process, the portion 29b of the hub axle 29 tends to be staked in an axial direction more than in a radial direction. As a result thereof, the axial deformation of the hub axle 29 becomes excessive, so that the hoop tension generated in the inner race 30 becomes high. Once the hoop tension becomes excessive, it causes cracking and/or premature exfoliation of the inner race 30.        (2) If the step 36 is formed large in the inner race 30, the area of abutment between the inner race 30 and the step 33b in the outer race 33 of the constant velocity universal joint becomes small, resulting in an excessive increase of the contact surface pressure. More precisely, when the inner member 22 is axially fastened with the outer race 33 and the nut 34, the end face of the inner race 30 and the step 33b of the outer race 33 are brought into contact. If the area of the end face of the inner race 30 is small, the contact surface pressure becomes large and it causes wear and/or abnormal noise after the bearing assembly is incorporated in the automotive vehicle.        
It is to be noted that with the wheel support bearing assembly in which the staked portion 29b is not provided in the hub axle 29, the problems (1) and (2) do not occur, but it may occur that the inner race may drop out under the influence of vibrations at a time subsequent to shipment of the bearing assembly and before installation on the automotive vehicle.